Split-brain studies of the 1960s gave birth to misuse of the left-brain right-brain theory by popular media, marketers, expert advisors, authors, educators, etc. who, e.g., devised methods to detect if a person is left-brain or right-brain dominant and provide training to the non-dominant side.

This came down to such levels that in one particular test, you just need to stare at the image of a spinning dancer (click on the accompanying image) for 30 seconds. If you see the dancer turning counter-clockwise, you’re left brained. If you see her turning clockwise, you’re right brained.

Spinning Dancer

Such blatant exploitation resulted into scientists strongly refuting the left-brain right-brain theory and blaming its simplicity for its popularity, calling it pop-science, pseudoscience, myth, etc.

Scientific support to refute the theory was provided by a two-year-long study by the University of Utah titled "An Evaluation of the Left-Brain vs. Right-Brain Hypothesis with Resting State Functional Connectivity Magnetic Resonance Imaging" published in August 2013, in which data from resting state brain scans of 1,011 people were analysed to test the veracity of left-brain right-brain theory.

The study resulted into the worldwide scientific community largely rejecting the Left Brain-Right Brain theory ever since, but was inherently flawed.

Following are the reasons:

The study was done to test veracity of the "Left-Brain vs. Right-Brain Hypothesis", which states that logical, analytical, detail oriented, rule based, etc. interactions are processed by the left hemisphere and creative, emotional, holistic, etc. interactions are processed by the right hemisphere (i.e. lateralized), but did not take into consideration any such interactions. Instead, it relied on inference from static brain structures, ignoring the dynamic properties of sequential functional processing of such diverse types of interactions (a crude example: with sleep and wake states being drastically different functional modes, do brain structures change when a sleeping person wakes up?)

The study inferred lateralization by observing connections between functional areas, which is a flawed method, because to detect lateralization, it is essential to detect in which hemisphere the processing of various interactions (or their sequential parts) are being initiated, i.e. hemisphere in which set of neurons are being activated. Inferring lateralization from connections (instead of the area of origin) can result into wrong conclusions, as revealed by the following example: If a set of neurons in the left hemisphere perform logical processing and send the resulting information to the right hemisphere for holistic processing, inferring from the connection between them will give the effect that both hemispheres are involved in such interaction (i.e. non-lateralized), which is what the study falsely concluded. In simpler words, if the cap of a bottle is produced in city A and the main body is produced in city B, the study’s conclusion is analogous to the bottle being made on the highway connecting the cities

Besides flawed methodology, the results of the study contradicted outcomes of various experiments carried out by Sperry and Gazzaniga, all of which are causally explained by the DOS model.

One of the researchers involved in the study made a statement that "It may be that personality types have nothing to do with one hemisphere being more active, stronger, or more connected". How sweeping the statement was can be demonstrated by the fact that as per the model, not only human personalities are driven by how the database in right hemisphere is built and utilized, but that such utilization has evolved based on gender specific execution strategies driven by the survival and reproduction goals of the evolutionary process, and that the institution of marriage is designed to optimize such goals, and that the differences in male and female behaviours, capabilities, traits, etc. are fallout of the same.

Without the causal backbone, certain key studies like the above mislead fundamental scientific research, pushing back progress in brain sciences by decades, as in the case of experiments carried out by neurophysiologist Benjamin Libet three decades ago, which ever since has resulted into the worldwide scientific community largely rejecting the view that humans have free will (more here).